The development of gastroduodenal ulceration after thermal injury is a life threatening complication, constituting the seventh leading cause of mortality in burned subjects. The emergent post burn period is characterized by a variety of systemic hemodynamic alterations, suggestion has been made that gastric mucosal microcirculatory alterations may predispose the mucosa to ischemia and subsequent acid-peptic proteolysis. The objectives of this investigation are to determine (1) whether there is a reduction in gastric mucosal blood flow via the opening of submucosal arteriovenous shunts, and (2) whether the adrenergic and cholinergic mechanisms play a major role in the distribution of mucosal blood flow. The rat is appropriate for study because the microvasculature of this species is comparable to human specimens and an ulcer rat burn model has been previously developed. Anesthetized rats will be subjected to a 30% body surface area scald burn by exposure for 15 seconds in hot water (90 degree C). To evaluate alterations in gastric mucosal blood flow as a post burn ulcerogenic factor the following experiments will be conducted in both the burn and control animals: (1) Gastric mucosal blood flow will be determined by the 14C aniline clearance technique at hourly intervals during the first 24 hour post burn period; (2) Gastric mucosal blood distribution will be assessed at hourly intervals following intra-aortic injection of india ink. Sections of the stomach will be mounted on slides and the optical densities measured. The third experiment will focus on adrenergic and cholinergic effects upon mucosal blood flow and ulcerogenesis in the burned animal model. Phenotolamine, Propranolol and atropine will be administered to series of rats following the burn and sham burn procedure to evaluate the effects of these drugs upon the gastric microvasculature.